Gastinger



April 22, 1958 E. GASTINGER 2,831,784

COATING PROCESS FORMING LAYERS OF GERMANIUM Filed Sept. 12, 1955 Mixture, of Ge ,0 and @608 12*; l

M/xtfure of GO and 60 EKKE AQD 64577/7662 INVE/Y TOR,

United States Patent COATING PROCESS FGRMING LAYERS 0F GERMANIUNI Ekkehard Gastinger, Paris, France, assignor to Centre National dEtudes des Telecommunications, lssy les Moulineaux, France, a French company Application September 12, 1955, Serial No. 533,557 Claims priority, application France December 30, 1954 4 Claims. (Cl. 117-201) The subject matter of the present invention is a new process which enables the smooth or wrinkled surface of a body to be coated with an homogeneous and adherent metallic layer of germanium.

The body to be coated should have a melting point of above 400 C. Many metals fulfill this condition, but they can be used only if the metallic coating does not combine with them to form an alloy.

Materials which are very suitable as a support for the metallic deposit are, for example, graphite, quartz and ceramic materials.

At the present time, there are numerous processes for manufacturing metallic coatings of germanium. Certain of these processes, such as the process of coating by electronic bombardment, necessitate expensive installations. Methods which utilise electrolytic phenomena have to be carried out with scrupulous care.

Other processes are suitable only for thick coatings. Among these there may be mentioned the process which consists in dipping the materials to be coated in a bath of molten metal and then working on the deposit obtained with a metallic brush.

Finally, certain methods necessitate the employment of too high temperatures. The best known of these methods consists in volatilising germanium, for example, in a chamber which has been raised to a temperature of over 1000" C. The vacuum in this chamber, which is equal to about millimeters of mercury, has to be very high, owing to the fact that germanium has a very low vapour pressure even in the liquid state. Metallised surfaces can also be obtained by vaporising, by decomposing, at over 1000 C., vapours of germanium tetrachloride in the presence of hydrogen.

The coating process according to the invention starts with incompletely purified germanium containing germanium dioxide. It is known to prepare germanium material for rectifiers and the like by reducing germanium dioxide to high purity germanium in a furnace which is flushed with pure hydrogen and heated to 650 C. for several hours and then to 1000 C. for at least one hour. It often happens that the whole ingot thus obtained is not of sufiicient purity for cutting the same into slices as are to be used in electronic circuit elements and constitutes waste material. The said material is the starting material of my coating process.

It does not need expensive plant. The manipulations are not diflicult. The temperatures used are below l000 C. and the vacuum, about 10 millimeters of mercury, is easy to maintain. Finally, it is possible to obtain coatings having a thickness that can be predetermined; the metallic deposit may be thin or of a thickness which may reach 2 millimeters and more.

The principle of the invention is as follows:

The body to be coated is placed in a chamber containing vapours of germanium monoxide. As the body is kept at a rather low temperature, condensation of the monoxide vapours on the surface takes place; the result of this is that it gradually becomes coated with a compact 2,831,784 Patented Apr. 22, 1958 homogeneous layer of germanium monoxide, the adhesion of which is comparable with that of a varnish. When the thickness of the deposit reaches the set amount, the body is placed in a current of hydrogen which reduces the monoxide, forming pure germanium and water in accordance with the equation The mixture of the metal and its normal oxide is transformed into monoxide, independent of the relative proportions in the mixture by heating it, at a temperature higher than 600 C. and under a pressure less than one atmosphere, in carbon dioxide mixed with carbon monoxide. The volatilized monoxide is carried along by the current of gas into a cold chamber, where it is deposited in the form of a black powder.

A feature of the present invention is that the monoxide used does not undergo any handling because the surface to be coated is placed in the apparatus which serves for the preparation of the monoxide.

In order to enable the invention to be better understood, reference will be made to the accompanying single figure.

It represents, by way of example, an apparatus provided for the purpose of coating, with germanium, small circular or square plates, the areas of the surfaces of which may be as much as 4 sq. ems.

The principal part of the apparatus consists of a tube 1 of quartz, the middle part of which is introduced into an electric furnace 2. The material to be converted into monoxide is arrange-d in a cupel 3 of refractory material. The latter is placed in the tube 1 at the centre of the electric furnace 2. Very near the cupel 3, the crosssectional area of the tube diminishes progressively so as to form a nozzle 4. The plate 5, which is to be coated with a metallic deposit, is placed opposite the small aperture of the nozzle 4. In addition, plate 5 is accommodated in a space 6 at the end of a metal cylindrical reservoir 7 containing water; the said reservoir is surrounded by the extension of the tube 1 beyond the nozzle 4. The circulation of water in the reservoir 7 is ensured by the tubes 8 and 9. The concentric part between the reservoir 7 and the tube 1 constitutes a low-temperature chamber in which the monoxide in excess is precipitated.

Fixed to the left-hand end of the tube 1 is a capillary tube 10 through which the tube 1 communicates with a gas reservoir 11 which contains a mixture of carbon dioxide and carbon monoxide.

A tube 12, which communicates with a vacuum pump 13, is soldered to the right-hand end of the tube 1. In addition, the tube 12 is provided with a capillary tube 14.

The vacuum pump 13 sucks the mixture of gases contained in the reservoir 11 through the intermediary of the reaction tube 1 and the capillary tube 10. There is thus a circulation of the monoxide vapours. The choice of the diameters of the capillary tubes 10 and 14 renders it possible to obtain the speed desired for the gaseous current without changing the normal rate of working of the pump.

The operation of the apparatus is as follows:

The plate to be coated is, after having previously been degreased, placed in its housing 6 opposite the end of the nozzle 4.

The germanium and germanium dioxide material to be converted into monoxide is placed in the cupel 3 and then heated by the electric furnace to a suitable temperature varying between 700 and 1000 C. according to the relative proportions of the two components. The vacuum pump 13 is started and produces the circulation of the mixture of gases in the tube 1. The proportion between the two gases CO and CO varies also with the relative proportions of the two components; this is also the case for the amount of pressure to be maintained in the tube 1 during the whole of the period of the chemical reaction.

At the end of a certain time, the plate 5, which is kept by the cooler 7 at a temperature of between 400 and 500 C., is coated with a certain layer of monoxide. When the thickness of the latter is judged to be sufficient, the apparatus is stopped. The cupel 3 is withdrawn: the reservoir 11 and the capillary tube as well as the pump 13 and the capillary tube 14 are removed; a current of hydrogen is then passed through and converts the monoxide condensed on the plate into gallium, germanium or indium. During this operation, the temperature of the plate rises and may reach 500 to 600 C.

By way of indication, there are given below the rules to be observed in order to obtain, under the best possible conditions, a layer of germanium containing 0.1% of indium, having a thickness of 2 millimeters and deposited on a quartz plate having a surface area of 4 sq. ems.

((1) Composition of the germanium and germanium dioxide material:

Equality of the two components weight treated: 5 grams.

Amount of significant impurities: 0.05% (i. e. 2.5 milligrams) of In O in the form of a fine powder.

Temperature of the furnace: 950 C.

Temperature of the quartz plate: 450 C.

Composition of the mixture of gases: 50% CO 50% CO.

Pressure in the tube during the reaction: millimeters of mercury.

Duration of the operation for a layer of a thickness of 2 mms.: minutes.

(b) Reduction of the monoxide by hydrogen:

Temperature of the furnace and of the quartz plate: 600 C.

Pressure in the tube during the reduction: 780 millimeters of mercury.

Duration of the reduction: minutes.

What I claim is:

l. A process of coating a layer of germanium onto a surface of a solid base body which is chemically and physically inert at temperatures between 400 C. and 600 C. and which does not form an alloy with germanium comprising producing volatile germanium monoxide in vapor form by heating a germanium and germanium dioxide material at a temperature above 600 C. and 1000 C. and under a pressure of less than one atmosphere in a stream of carbon dioxide and carbon monoxide, condensing said volatile monoxide on said surface of said solid base at a temperature below 600 C. in the form of a homogeneous solid adherent layer of monoxide which completely covers said surface and reducing said germanium monoxide layer at a temperature of about 4 500 C.600 C. to the corresponding germanium metal layer by reacting with a current of reducing gas at a pressure which is substantially atmospheric pressure.

2. A process of vacuum coating a layer of germanium onto a surface of a solid base body which is chemically and physically inert at temperatures between 400 C. and 600 C. and which does not form an alloy with germanium comprising producing germanium monoxide in vapor form by heating a germanium and germanium dioxide material at a temperature above 600 C. and 1000 C. and under said vacuum in a stream of carbon dioxide and carbon monoxide, condensing said volatile monoxide on said surface of said solid base at a temperature below 600 C. in the form of a homogeneous solid adherent r layer of monoxide which completely covers said surface and reducing said germanium monoxide layer at a temperature of about 500 C.-600 C. to the corresponding germanium metal layer by reacting with a current of reducing gas at a pressure which is substantially atmospheric pressure.

3. A process as claimed in claim 1 wherein the solid base body to be coated is selected from the group consisting of ceramic, quartz and graphite.

4. A process of vacuum coating a layer of germanium onto a surface of a solid base body which is chemically and physically inert at temperatures between 400 C. and 600 C. and which does not form an alloy with germanium comprising producing volatile germanium monoxide in vapor form by heating a germanium and germanium dioxide material at a temperature of about 950 C. and under a pressure of about 10 millimeters of mercury in a stream of about 50% carbon dioxide and 50% of carbon monoxide, condensing said volatile monoxide on said surface of said solid base at a temperature below 600 C. in the form of a homogeneous solid adherent layer of monoxide which completely covers said surface and reducing said germanium monoxide layer at a temperature of about 500 C.-600 C. to the corresponding germanium metal layer by reacting with a current of reducing gas at a pressure which is substantially atmospheric pressure.

References Cited in the file of this patent UNITED STATES PATENTS 1,884,665 Geriner Oct. 25, 1932 2,241,438 Zischkan et a1 May 13, 194] 2,552,626 Fisher et al May 15, 1951 2,576,267 Scafi' et al Nov. 27, 1951 2,692,839 Christensen et al Oct. 26, 1954 OTHER REFERENCES Transactions American Electro Chemical Society, vol. 89 (1946), p. 279, Germanium Digest. 

1. A PROCESS OF COATING A LAYER OF GERMANIUM ONTO A SURFACE OF A SOLID BASE BODY WHICH IS CHEMICALLY AND PHYSICALLY INERT AT TEMPERATURES BETWEEN 400*C. AND 600*C. AND WHICH DOES NOT FORM AN ALLOY WITH GERMANIUM COMPRISING PRODUCING VOLATILE GERMANIUM MONOXIDE IN VAPOR FORM BY HEATING A GERMANIUM AND GERMANIUM DIOXIDE MATERIAL AT A TEMPERATURE ABOVE 600*C. AND 1000*C. AND UNDER A PRESSURE OF LESS THAN ONE ATMOSPHERE IN A STREAM OF CARBON DIOXIDE AND CARBON MONODIDE, CONDENSING SAID VOLTAGE MONOXIDE ON SAID SURFACE OF SAID SOLID BASE AT A TEMPERATURE BELOW 600*C. IN THE 